The use of the meters for monitoring blood glucose levels is a well established means of improving insulin control for diabetic persons. Other applications of reflectance meters for measuring remission characteristics or diffuse reflection characteristics of a chemically treated reagent strip are also well known. A typical reflectance meter includes a light source for illuminating a target, a photo-detector for detecting light reflected from the target, and reagent strip targets which provide an indication of chemical makeup of a solution. The target strips provide a color change which corresponds with a particular chemical concentration in such a fashion that a very repeatable color change occurs when a particular concentration of a target chemical in solution is detected. Normally, the light source and the light detector are keyed to a particular wavelength of light or range of wavelengths so as to accurately measure the color change in the reagent treated strip. The wavelength of light corresponding to the color to be detected and produced by the strip may be in the visible light range or outside the visible light range in the infrared region. It is also well known that electro-magnetic radiation or light having identical wavelengths are also found in ambient light or sunlight as well as in artificial light produced by electrical light fixtures. The reliability and repeatability of a reflectance meter is seriously impacted by extraneous light which creates electronic noise in the measured signal. A reflectance meter which incorporates circuitry to reduce or eliminate the effects of ambient and artificial lighting is needed.